This application claims priority of Great Britain Patent Application No. 0020581.5, which was filed on 21st Aug. 2000.
1. Field of the Invention
This invention relates to an improved method of operating a mobile telecommunications network, especially a method of addressing packets destined for a mobile terminal in a foreign network.
2. Description of Related Art
In third generation telecommunications networks such as GPRS (General Packet Radio Service) and EDGE (Enhanced Data-rate for GSM Evolution), when a mobile terminal moves into a foreign network, network connectivity is optionally maintained by the use of Mobile Internet Protocol (Mobile IP). In the home network, a Home Agent (HA) is set up which maintains the location information of the mobile by use of Binding Updates, i.e., registration of information sent to the HA by the mobile node.
Mobile IP has two working modes. The first is illustrated in FIG. 1; a mobile terminal is currently attached as Mobile Node (MN) 14 in a network different from its home network. The MN 14 is communicating with a Correspondent Node (CN) 12. A Home Agent 16 is set up in the home network by the CN 12, and a Foreign Agent (FA) 18 is set up in the foreign network. The FA 18 allocates a unique IP address for the visiting mobile, a Care of Address (COA) and this address is sent to the HA 16 in a Binding Update.
Packets for the mobile are encapsulated by the HA 16 and tunnelled along tunnel 20 to the FA 18 for transmission to MN 14. In such encapsulation, an extra IP header is added to each packet, including the COA of the MN 14. This is known as FA-COA working mode.
In the second working mode (not illustrated) there is no FA, the MN 14 is allocated a unique COA and encapsulated packets are tunnelled by HA 16 directly to MN 14; this is known as Colocated Care of Address mode of working (CO-COA).
In both FA-COA and CO-COA modes of working, the encapsulation generates extra headers, and possibly only small payloads can be used, which results in inefficient transmission and inefficient use of expensive system and network resources, such as radio links. Further, encapsulation hides the flow identification, and the differentiation of classes of services is thus also disabled, so that Quality of Service (QoS) provision mechanisms, such as RSVP (Resource reSerVation Protocol) Int Serve, must be changed.
The disadvantages of encapsulation can be avoided by the use of Non Encapsulation Mobile IP technique, as set out in the applicant""s co-pending patent application xe2x80x9cNon-encapsulation Mobile IPxe2x80x9d filed on 26 Feb. 1999 as no. 99301437.2. In this technique, the current COA of the mobile node is used as the destination address, and the original source address, i.e. the CN address, is maintained. For FA-COA working, this deletes a header of length at least 20 bytes and introduces a header of only 2 bytes; for CO-COA mode of working no header is introduced. However a disadvantage is that any firewall or egress filtering in the home network may reject such packets, because they have a source address different from the home network address.
It is an object of the invention to provide a method of packet addressing which overcomes the disadvantages set out above, and allows QoS to be provided.
According to the invention, a method of providing quality of service in a third generation mobile telecommunications system, in which packets are addressed to a mobile node which has a correspondent node in a home network and which is currently associated with a foreign network characterized by the steps of
sending a quality of service enquiry message from the correspondent node to the home network;
sending said quality of service enquiry message from the home network to the mobile node;
sending a quality of service response message from the mobile node to the home network by the same route as the enquiry message;
and sending a quality of service response message from the home network to the correspondent node only after receipt of the quality of service response message from the mobile node.